1. Field of the Disclosure
This disclosure relates to a liquid crystal display device with a backlight unit configured to realize a slim size and a uniform luminance.
2. Description of the Related Art
With an increase in information dispersion in society, display devices capable of displaying information have been developed. These display devices include liquid crystal display (LCD) devices, organic electro-luminescence display devices, plasma display devices, and field emission display devices. LCD devices tend to be lighter and smaller and can provide a low power drive and a full color scheme. Accordingly, LCD devices have been used for numerous applications, such as mobile phones, navigation systems, portable computers, televisions, etc.
The LCD device utilizes a backlight unit capable of irradiating light for the display as it is otherwise not luminous. The LCD device controls the transitive amount of light irradiated from the backlight unit for displaying images.
FIG. 1 is a cross sectional view showing a backlight unit of edge type according to the related art. As shown in FIG. 1, the edge type backlight unit 10 includes a fluorescent lamp 12 disposed at the side of a light guide plate 11, a reflection sheet 14 disposed under the light guide plate 11, and optical sheets 15 disposed over the light guide plate 11.
The fluorescent lamp 12 emits light that enters into the light guide plate 11. However, some of the light emitted in the fluorescent lamp 12 may not enter into the light guide plate 11 resulting in light leakage. In order to prevent or minimize the light leakage, a lamp housing 13 with reflective properties is provided to surround the fluorescent lamp 12. Accordingly, some of the light emitted from the fluorescent lamp 12 directly enters into the light guide plate 11, while the rest of light is reflected by the lamp housing 13 towards the light guide plate 11.
Light within the light guide plate 11 progresses toward the optical sheets 15 directly or by being reflected from the reflection sheet 14. The optical sheets 15 allow light to be diffused and irradiated to a liquid crystal panel (not shown) above the optical sheets 15.
FIG. 2 illustrates another backlight unit 20 of direct type that includes a reflection sheet 24 disposed on a bottom cover 23, a plurality of fluorescent lamps 22 arranged on the reflection sheet 24, and optical sheets 25 stacked over the fluorescent lamps 22. Another optical sheet 21 is disposed between the optical sheets 25 and the fluorescent lamps 22.
The edge type backlight unit, which includes the fluorescent lamp disposed at one side of the light guide plate may have display problems. A deviation in brightness may be generated between regions of the light guide plate adjacent to and remote from the fluorescent lamp. In other words, the brightness may not be uniform across the display. This problem may be worse as the size of the liquid crystal panel is increased.
In the direct type backlight unit, the shapes of the fluorescent lamps may appear on the liquid crystal panel to the viewer. To reduce the effect of the fluorescent lamps being revealed on the liquid crystal panel, the distance between the fluorescent lamps and the optical sheets may be increased. However, increasing the distance between the lamps and the optical sheets results in a backlight unit that is thicker, thereby making it more difficult to produce an LCD device that is slim.